Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful behavioral context – the $0.05 USDC x402 charge per successful call and the two supported chains – but says nothing about what happens on an invalid or non-existent DDD, which matters for a paid call.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two short sentences: return content first, then the payment condition. Nothing is redundant and the most important fact leads.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With one fully described parameter and no output schema, the description tells the agent what the response contains and what it costs, which covers most of what is needed. The gap is failure behavior for invalid codes on a paid endpoint.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and the single parameter is already documented as a '2-digit DDD' in the schema. The description only restates 'area code (DDD)' without adding format, validation, or example guidance, so baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names the resource (Brazilian area code / DDD) and the exact return fields (state, cities, time zone), so an agent knows precisely what it gets back. It stops short of naming a verb or distinguishing it from the nearest siblings like phone_lookup or osint-phone, which also deal with phone numbers.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

There is no statement of when to use this tool versus br_cep, phone_lookup, or osint-phone, nor any exclusion for non-Brazilian numbers. The only usage-adjacent content is the payment note, which is about cost, not selection.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.